This invention relates to a decoating device, for precoated printing plates developed with liquid toner, having pairs of conveyor and squeezing rollers between which the printing plates pass, and having a spray device for spraying decoating liquid onto the developed surface of the individual printing plates.
Printing plate processing units of compact construction, as manufactured by KALLE Niederlassung der Hoechst AG, are known, by which printing plates are decoated or developed, rinsed, fixed/gummed and dried in one pass. In a decoating apparatus of the above type, the decoating agents and the rinsing water are kept in constant circulation by circulating pump units. Because of the closed circuits for the decoating liquid and the rinsing water, permanent connections to a water pipe and drain are unnecessary, so that the known decoating apparatus can be set up at any site. Other types of known printing plate processing units develop, rinse, fix/gum and dry the printing plates in one pass. These devices are, for example, fitted with an automatic topping-up system for the developer concentrate to stabilize the developer which circulates in a closed circuit inside the apparatus. The developer is cooled by a continuous water cooling system which is thermostatically monitored. The developer temperature is regulated by means of a thermostatically monitored developer heating system.
The processing of plates on the printing plate processing units is matched to the particular requirements by an independent speed adjustment for the plate pass and for the scrubbing elements such as, for example, brush rollers or plush-covered rollers.
It is common to the known printing plate processing units that a limited number of plates are decoated or developed with a specified quantity of decoating liquid. The number of printing plates is limited by saturation of the decoating liquid with coating residues. With increasing viscosity of the decoating solution, the pass speed of the printing plates has to be reduced in order to achieve satisfactory decoating or development. Also, although the decoating rate increases with rising temperature, limits are imposed on the temperature rise as a relatively large quantity of liquid has to be heated up, which requires a certain time. In addition, the risk of scalding through incorrect handling of the printing plates increases as a result of the higher temperatures of the decoating liquid. Because of the closed decoating liquid circuits in the known devices, printing plates which require different decoating or developing liquids for decoating or developing can only be processed after carrying out appropriate conversion work in each case.